Compact rotary switch

Abstract: A rotary switch includes a plurality of switching terminals (28a-28e) exposed within a chamber in a housing (22). A fixed planar contact member, having a plurality of spring contact arms (56a,56b,58a,58b), is mounted in the chamber above the terminals. Each of the contact arms is movable out of the plane of the contact member to contact an associated one of the terminals. Each of the contact arms includes a cam follower (60a,60b,62a,62b), at least two of the cam followers being equidistant from the center of the contact member. The cam followers are operatively engaged, in a predetermined sequence, by camming elements extending axially from the bottom surface of a rotor mounted in the chamber above the contact member. The equidistant cam followers are engaged by camming elements that are spaced from the center of the rotor by a distance equal to the distance separating the equidistant cam followers from the center of the contact member. Thus, at least two contact arms are actuated by camming elements sharing a common radius, thereby allowing the optimum use of space. The contact member is fixed in the chamber by a set of asymmetrical tabs that are received in slots in the chamber wall, thereby preventing an inadvertent erroneous orientation of the contact member during assembly.

Description: Background of the Invention This invention relates generally to the field of rotary switches. More specifically, it relates to a rotary encoding switch, of the type having a stationary contact spring element with multiple spring contact fingers that are urged axially into engagement with selected coded terminal elements by an arrangement of axial cams on the underside of a rotor. Rotary encoding switches, of the type mentioned above, are known in the art. See, for example, U.S. Patent No. 4,400,597 - Bruder et al.; U.S. Patent No. 5,008,498 - Yamazaki; and U.S. Patent No. 5,010,214 - Yamazaki. In such switches, a stationary spring contact, or "spider", having multiple spring contact arms, is fixed within a housing between a rotor and a plurality of fixed coded electrical terminals, so that the spring arms are axially movable to make and break electrical contact with the terminals. A rotor is provided with a plurality of axially-extending camming elements on the surface facing the spider. As the rotor is turned, the camming elements are brought into and out of engagement with cam follower structures on each of the contact arms, whereby the arms are displaced axially into contact with a selected terminal as the rotor is turned, in accordance with the pattern of the camming elements. When the cam follower structure on an arm is not engaged by a cam, the resilience of the arm causes it to move axially out of engagement with the terminal, thereby breaking contact therewith. There has been a long term trend for higher degrees of miniaturization of electronic components. Consistent with that trend, components such as rotary switches have been substantially reduced in size, and further size reductions are still demanded. For example, surface mounted components, including rotary switches, are now commonly made smaller than 10 mm on a side, and components of as little as 4 to 5 mm on a side are in increasing demand. The structure of the prior art rotary switches, of the type described above, makes such ultra-miniaturization difficult to achieve while maintaining performance criteria, such as accuracy and reliability. For example, the device described in the above-referenced patent to Bruder et al. employs a spider having radial contact arms of substantially uniform total length, each having a single cam follower tab. Each of the tabs is located at a different unique radius, for actuation by a cam lobe located at the corresponding radius on the facing surface of the rotor. Electrical contact between the contact arms and the switching terminals occurs at the ends of the contact arms. This radial contact arm structure, and the need to have one contact arm dedicated to each camming radius, lead to an inefficient use of space that imposes limits on the degree of miniaturization that can be achieved. A more efficient use of space is obtained in the devices described in the above-referenced patents to Yamazaki. These devices employ a stationary contact or spider having the configuration shown in Figure 1 attached to the present specification. As shown, the prior art spider 10 includes a plurality of contact arms 12a, 12b, 12c, 12d, and 12e, arranged circumferentially, rather than radially. Each contact arm 12a - 12e is located at a different radial distance from the center of the spider, and is actuated by a rotor-mounted camming element (not shown) that is located at the same radial distance from the center of the rotor, and that operates on its associated contact arm through a cam follower projection 14 on the arm. In other words, each camming element, at its unique distance from the center of the rotor, operates on a single contact arm located at the same radial distance from the center of the spider. In a binary coded switch, each binary bit (i. e., 1, 2, 4, 8, etc.), is defined by a unique camming element operating only on its associated contact arm. Thus, each bit requires its own unique operational camming element/contact arm radius, thereby requiring either spiders and rotors of larger radii, or smaller (and more delicate) contact arms and camming elements, as the number of bits is increased. In addition, for any given number of bits, size can be reduced only by reducing the width of the contact arms and reducing the size and spacing between the camming elements, thereby possibly compromising durability and reliability. In short, if further miniaturization is desired, one must either reduce the width of each contact arm, or limit the number of contact arms. If the former course action is employed, durability and reliability may be compromised, and manufacturing costs may be increased. If the latter strategy is used, the number of switching values may be limited. It would therefore be desirable, if maximum efficiency in space utilization is the goal (as it is in ultra-miniaturization), to arrange the contact arms and the associated camming structures so that more than one contact arm is located at a single radial distance from the center of the spider, so as to be actuated by one or more camming structures located at that same radial distance from the center of the rotor. Summary of the Invention The present invention is defined in the appended Claim 1, whose preamble is based on US-A-5 008 498. In other words, there is provided a multi-position rotary switch having a stationary conductive contact member, or "spider", with multiple spring contact arms, that is fixed in a housing between a rotor and a plurality of fixed coded electrical switching terminals. The spider is fixed in place in the housing at first and second end portions. The preferred embodiment has an inner pair of contact arms and an outer pair of contact arms, arranged symmetrically with respect to a common or ground contact finger at the center of the spider. The inner contact arms extend in a first direction from the first end portion toward the second end portion, while the outer contact arms extend in a second direction from the second end portion toward the first end portion. Each of the contact arms has a cam follower protuberance, thereby providing inner and outer pairs of cam followers. The cam followers on the inner arms are equidistantly spaced, at a first radial distance, from the center of the spider on opposite sides thereof, while the cam followers on the outer arms are equidistantly spaced, at a second radial distance greater than the first radial distance, from the center of the spider on opposite sides thereof. Thus, at each of the first and second radial distances from the center, there are two cam followers. The cam followers at each of the first and second radial distances are operatively engaged by one or more camming elements on the facing surface of the rotor, which are at the corresponding radial distance from the center of the rotor. As the rotor is rotated to selected rotational positions, each of which corresponds to a numerical value, the cam follower protuberances at each radial distance from the center are operatively engaged by each of the camming elements at that same radial distance, in accordance with a preselected sequence dictated by the arrangement of the camming elements and the cam follower protuberances. The engagement of a protuberance by a camming element results in the actuation of the contact arm on which the protuberance is located, by means of the bending of the contact arm axially out of the plane of the spider. Each contact arm represents a unique binary bit, and, when actuated by a camming element, is brought into electrical contact with one of the coded switching terminals, producing an output signal representing that bit. The contact arms and camming elements are arranged so that a 360° rotation of the rotor yields the sequential actuation of the contact arms in combinations that produce binary coded signals representing all the integral numerical values within a range determined by the number and arrangement of the camming elements. For example, in a preferred embodiment of the invention, there are four contact arms, one for each binary bit from "1" to "8", arranged symmetrically, as described above, around a center "common" contact. A first pair of contact arms, representing the "4" and "8" bits, respectively, are located on opposite sides of the center, with their cam followers at a first radial distance from the center. The contact arms in the first pair extend in a first direction, and respectively make electrical contact with terminals representing the numerical output values of "4" and "8" when actuated (that is, axially displaced) by a first set of camming elements located at the same radial distance from the center of the rotor. A second pair of contact arms, representing the "1" and "2" bits, respectively, are located on opposite sides of the center, with their cam followers at a second radial distance from the center, which is greater than the first radial distance. The contact arms in the second pair extend in a second direction, and respectively make electrical contact with terminals representing the numerical output values "1" and "2" when actuated by a second set of camming elements radially separated from the first set of camming elements by a radial distance equal to the radial separation between the inner and outer pairs of cam followers. With this arrangement, up to 10 binary coded numerical output values can easily be obtained, depending on the number and arrangement of the camming elements in each set. Greater numbers of numerical output values can be obtained with relatively minor modifications in the contact arm and camming element arrangements. With the arrangement of more than one contact arm, each representing a different binary bit value, actuated (by means of its camming protuberance) at a given radial distance from the center of the stationary contact element or spider, optimum usage of space is achieved. As a result, a very high degree of miniaturization can be obtained, without sacrificing durability or reliability. For example, a binary coded switch having as many as 10 (and possibly more) numerical output values can be provided in a housing as small as 4 to 6 mm on a side, with contact arms and camming elements that are of substantial enough construction to endure relatively long term use, undergoing a large number of rotational cycles without significant loss of structural integrity. The rotor is retained in the housing by a retention casing that is secured to the sides of the housing, and that has a central aperture in its top surface through which the central portion of the top of the rotor is exposed. The top surface of the rotor is provided with a plurality of radial detent grooves that extend toward the peripheral edge of the rotor. A resilient detent member is located on the retention casing so as to engage the detent grooves sequentially as the rotor is rotated, thereby providing a detented position for each numerical output value. The advantages mentioned above, and others, will be more fully appreciated from the detailed description that follows. Brief Description of the Drawings Figure 1 is a top plan view of a stationary contact member, of the type used in a prior art rotary switch; Figure 2 is a cross-sectional view of a rotary switch in accordance with a preferred embodiment of the invention; Figure 3 is a top perspective view of a stationary contact member, of the type employed in a preferred embodiment of the invention; Figure 4 is a top perspective view of a rotor of the type employed in a preferred embodiment of the invention; Figure 5 is a bottom plan view of the rotor of Figure 4, as configured in an eight-position binary coded rotary switch; Figure 6 is a side elevational view of the rotor of Figure 4; Figure 7 is a top perspective view of a rotor retention casing of the type employed in a preferred embodiment of the invention; Figure 8 is a top perspective view of a housing, with an array of electrical lead terminations disposed therein, as employed in a preferred embodiment of the invention; Figure 9 is an exploded perspective view of a rotary switch in accordance with a preferred embodiment of the invention; Figure 10 is a top plan view of the electrical lead terminations employed in a preferred embodiment of the invention, as viewed through the housing with the rotor removed; Figure 11 is a top plan view of the rotor retention casing of Figure 7, marked for use in an eight-position binary coded rotary switch; Figure 12 is a top plan view, similar to that of Figure 10, but with the stationary contact member of Figure 3 superimposed on the lead terminations; Figure 13 is a table showing the combination of contact arms of the contact member that is actuated for each of the eight positions in an eight-position binary coded switch constructed in accordance with the present invention; Figure 14a is a bottom plan view of the rotor, similar to that shown in Figure 5, but with the stationary contact member of Figure 3 superimposed thereon, the position of the rotor relative to the contact member being that which corresponds to the numerical values of "0" or "8"; Figure 14b is a view similar to that of Figure 14a, but with the rotor rotated to a position that corresponds to the numerical value of "3"; Figure 14c is a view similar to that of Figures 14a and 14b, but with the rotor rotated to a position that corresponds to the numerical value of "7"; Figure 15 is a bottom plan view of a rotor as configured for use in a ten-position binary coded switch; Figure 16 is a bottom plan view of the rotor of Figure 15, but showing the stationary contact member of Figure 3 superimposed thereon, the position of the rotor relative to the contact member being that which corresponds to the numerical values of "0" or "10"; and Figure 17 is a table showing the combination of contact arms of the contact member that is actuated for each of the ten positions in a ten-position binary coded switch constructed in accordance with the present invention. Detailed Description of a Preferred Embodiment Referring now to Figures 2 through 12, a binary coded rotary switch 20, in accordance with a preferred embodiment of the present invention, will now be described in detail. The switch 20 comprises a thermoplastic housing 22 molded onto a lead frame 24, preferably formed from silver-plated phosphor-bronze. As best shown in Figure 8, the housing 22 defines a generally circular cavity or chamber 26 that is open at the top. The lead frame 24 defines a plurality of switching terminals 28a, 28b, 28c, 28d, 28e (Figure 10), arranged in a predetermined pattern (described below), that are exposed at the bottom of the chamber 26. The chamber 26 has a stepped-in, substantially annular side wall that defines an annular shoulder 30, on which is seated an O-ring 32. A rotor 34, to be described in detail below, is disposed for rotational movement in the chamber 26, the O-ring 32 providing a seal between the rotor 34 and the housing 22. Below the shoulder 30, on the chamber side wall, are first and second diametrically-opposed arcuate lips 36a, 36b, respectively. The chamber wall above the first lip 36a has an axial slot 38a. A pair of asymmetrical axial slots 38b are formed in the wall above the second lip 36b, as best shown in Figure 10. The asymmetry of the slots 38b may be achieved by spacing them differently with respect to the center of the second lip 36b, or by making the slots 38b of different sizes (arc lengths), as shown. It may be advantageous, as will be seen below, to provide a vertical post or boss 40, of a height equal to that of the tops of the lips 36a, 36b, extends upwardly from the bottom of the chamber 26, between the center of the chamber and the second lip 36b. As shown in Figure 3, a stationary contact member or spider 42 (described in detail below) is fixed in the housing 22 between the rotor 34 and the lead frame terminals 28a-28e. The spider 42 has first and second diametrically-opposed end portions 44a, 44b that respectively seat on the first and second arcuate lips 36a, 36b in the chamber 26, for proper axial spacing of the spider 42 from the rotor 34 and the terminals 28a-28e. The vertical post 40 provides support for the central portion of the spider. A pair of tabs 46, extending outwardly from the second spider edge 44b, are received in the slots 38b in the wall above the second lip 36b, while a single tab 48 extending outwardly from the first spider edge 44a is received in the slot 38 above the first lip 36a. The engagement between the single tab 48 and the slot 38, and between the double tabs 46 and the slots 38b, restrains the spider 42 from rotational movement within the chamber 26. The asymmetrical spacing of the double tabs 46 with respect to the second lip 36b assures that the spider cannot be inadvertently installed upside-down, while the use of a single tab 48 at one edge and double tabs at the other edge assures that the spider cannot be installed backwards. The spider 42 includes a resilient central contact finger 50 having a free end that is axially aligned with the approximate center of the spider, but angled axially out of the plane of the spider. The central contact finger 50 serves as a common or ground contact, and is maintained in electrical contact with one of the switching terminals (designated by the numeral 28a) that serves as a common terminal. (See Figures 8, 10, and 12.) The spider 42 includes a first, or inner, pair of resilient spring contact arms 56a, 56b, and a second, or outer, pair of resilient spring contact arms 58a, 58b, arranged symmetrically with respect to the central contact finger 50. The inner contact arms 56a, 56b extend in a first direction from the first spider end portion 44a toward the second spider end portion 44b, while the outer contact arms 58a, 58b extend in a second direction from the second end portion 44b toward the first end portion 44a. A pair of inner cam follower protuberances 60a, 60b are respectively provided on the inner contact arms 56a, 56b, and a pair of outer cam follower protuberances 62a, 62b are respectively provided on the outer contact arms 58a, 58b. The inner cam followers 60a, 60b are equidistantly spaced from the center of the spider, on opposite sides thereof, at a first radial distance from the center. The outer cam followers 62a, 62b are equidistantly spaced from the center of the spider, on opposite sides thereof, at a second radial distance from the center greater than the first radial distance. Thus, at each of the first and second radial distances, there are two cam followers. Each of the contact arms 56a, 56b, 58a, 58b has a downturned free end or contact 64 that establishes electrical contact with a corresponding switching terminal when the contact arm is actuated in the manner described below. As illustrated in Figures 2, 4, 5, and 6, the rotor 34 is a generally disc-shaped element of insulating material, such as a thermoplastic, having a stepped side wall 66 that creates a sealing engagement with the O-ring 32, while allowing the rotor to be rotated with respect to the housing 22. The axis of rotation of the rotor 34 is at least approximately coincident with the geometric center of the spider 42. The top or external surface of the rotor has a central area 68 that is divided into two substantially semicircular portions by a diametric slot 70, dimensioned and located to receive a tool (not shown) for rotating the rotor 34. Forming the periphery of the rotor's external surface is an annular peripheral flange 72 that seats against an adjacent surface of the O-ring 32. Extending between the central area 68 and the flange 72 are a plurality of radial detent grooves 74. The bottom or interior surface of the rotor 34 (Figures 5 and 6) is provided with a first plurality of axially-extending inner camming elements 76, and a second plurality of axially-extending outer camming elements 78. The inner camming elements 76, which are substantially conical in shape, are located at a first radial distance from the center of the rotor 34 that is equal to the first radial distance separating the inner cam followers 60a, 60b from the center of the spider 42. They thus are located so as to operatively engage the inner cam followers. The outer camming elements 78, which resemble axially-tapered arcuate ridges, are located at a second radial distance from the center of the rotor 34 that is equal to the second radial distance separating the outer cam followers 62a, 62b from the center of the spider. They are thus located so as to operatively engage the outer cam followers. Thus, by definition, the distance separating the inner camming elements 76 from the outer camming elements 78 is equal to the distance separating the inner cam followers 60a, 60b from the outer cam followers 62a, 62b. As will be discussed in detail below, the arrangement of the camming elements 76, 78 shown in Figure 5 is for an eight-position rotary switch. As shown in Figures 2, 7, and 9, the rotor 34 is retained in place by a casing 80, which may be formed of a metal stamping. As best shown in Figure 7, the casing has a substantially planar upper portion 82 with a central aperture 84, through which the central area 68 of the rotor 34 is exposed. The upper portion 82 engages the peripheral flange 72 of the rotor, seating the latter against the O-ring 32, as shown in Figure 2. A pair of side portions 86 depend downwardly from two opposed sides of the upper portion 82, so as to engage two opposed side walls 88 of the housing 22. Each of the side portions 86 has a straight-edged aperture or window 90. The corresponding side walls 88 of the housing are each provided with an integral locking projection 92 that extends outwardly therefrom, so as to register with the corresponding window 90, thereby providing a locking engagement between the housing 22 and the casing 80. The side edges of the casing 80 from which the side portions 86 do not depend are advantageously formed with a down-turned lip 94 that engages the adjacent housing surface for a more secure grip between the casing 80 and the housing 22. The upper portion 82 of the casing 80 is provided with an arcuate slit 96, adjacent to, and concentric with, the central aperture 84. An arcuate strip 98, narrow enough to flex resiliently, is thereby formed between the slit 96 and the central aperture 84. At the approximate center of the strip 98 a downwardly-extending detent projection 100 is formed. The detent projection 100 resiliently engages the detent grooves 74 in the top of the rotor 34, to provide a plurality of detented positions, and to provide a tactile indication of rotor rotation. Figure 11 illustrates a casing 80, in which the top portion 82 is marked to indicate eight binary-coded positions (0-7). Figure 10 illustrates the layout, within the housing 22, of the switching terminals 28a, 28b, 28c, 28d, and 28e for either' an eight-position or a ten-position rotary switch. The switching terminal 28a terminates a common or ground lead 102a, and it corresponds to a binary-coded value of "0". The other switching terminals 28b, 28c, 28d, and 28e terminate output leads 102b, 102c, 102d, and 102e, respectively, and they correspond to binary-coded output values of "1", "2", "4", and "8", respectively. (The switching terminal 28e and its associated lead 102e, corresponding to the output value of "8", are not employed in an eight-position switch, although these components may physically be present.) The output leads 102a-102e may be trimmed and bent under the housing 22, as shown in Figure 2, to provide a surface-mount configuration. Figure 12 illustrates the relationship, in either an eight-position or a ten-position switch, between the contact elements of the spider 42 and the switching terminals 28a through 28e when the spider is installed in the housing as described above. Specifically, the central contact finger 50 is maintained in contact with the common switching terminal 28a, so that there is always a common or ground connection representing a "0" value. A first one 58a of the outer contact arms is disposed so as to be overlying, but normally spaced from, the switching terminal 28b corresponding to the output value of "1". A second one 58b of the outer contact arms is similarly disposed with relation to the switching terminal 28c corresponding to the output value of "2". Likewise, a first one 56a of the inner contact arms overlies, but is normally spaced from, the switching terminal 28e corresponding to the output value of "8", while a second one 56b of the inner contact arms is similarly disposed with relation to the switching terminal 28d corresponding to the output value of "4". In general terms, the operation of the above-described preferred embodiment of the invention (whether an eight position or a ten-position switch) may be described as follows: Rotation of the rotor 34 (by a suitable tool, not shown) causes the camming elements 76, 78 to engage, in a predetermined sequence dictated by their shapes and location, the cam followers 60a, 60b, 62a, 62b. The operative engagement between a camming element and a cam follower causes the contact arm on which the engaged cam follower is located to flex axially out of the plane of the spider 42, bringing its contact end 64 into electrical contact with its adjacent associated switching terminal. The closure of a contact 64 with an associated switching terminal produces an output signal indicative of the numerical value to which that switching terminal corresponds. Thus, for example, the actuation of the contact arm adjacent to the "1" switching terminal produces an output signal indicative of the numerical value of "1". Output signals indicative of the numerical values of "2", "4", and "8" are similarly produced by the actuation of the contact arms adjacent to the switching terminals respectively corresponding to these values. Output signals indicative of the values "3", "5", "6", and "7" (and "9" in a ten-position switch) are produced by the simultaneous actuation of two or more contact arms. A value of "0" is obtained when none of the movable contact arms are actuated, leaving only the central contact finger 50 in electrical contact with the common or ground terminal 28a. The operation of an eight-position position switch in accordance with the above-described preferred embodiment is illustrated in Figures 13, 14a, 14b, and 14c. Figure 13 is a table that shows the combinations of switching terminals that, when closed by a contact arm, produce output signals representing each of eight binary-coded numerical values. The switching terminals corresponding to the values of "1", "2", and "4", and the common or ground terminal ("C") are displayed horizontally, while the numerical output values 0-7 are displayed vertically. An "X" indicates a closed terminal. It is seen that the common terminal is always closed, for all output values, and only the common terminal is closed for the output value of "0". For the other output values of "1" through "7", one or more of the "1", "2", and "4" terminals are closed, in addition to the common terminal. The "8" terminal is never closed, since its associated contact arm remains unactuated in an eight-position switch, in which only output signal values of "1" through "7" are used. Figure 14a shows the juxtaposition between the camming elements 76, 78 and the cam followers 60a, 60b, 62a, 62b in an eight-position switch when the rotor is rotated to a position to output a "0" value. As shown, none of the cam followers 60a, 60b, 62a, 62b is engaged by any of the camming elements 76, 78, leaving all of the contact arms 56a, 56b, 58a, 58b unactuated, and all of the switching terminals 28b-28e open. In Figure 14b, the rotor 34 has been rotated to a position to output a value of "3". In this position, the cam follower 62a on the outer contact arm 58a, corresponding to the output value of "1", is operatively engaged by one of the outer camming elements, so that the switching terminal 28b is closed to produce an output signal indicative of the value "1". Likewise, the cam follower 62b on the other outer contact arm 58b is operatively engaged by another of the outer camming elements 78 to close the switching terminal 28c, thereby producing an output signal indicative of the value "2". The algebraic sum of the two output signals is indicative of the value "3". Neither of the cam followers 60a, 60b on the inner contact arms 56a, 56b is engaged by any of the inner camming elements 76, thereby leaving open the switching terminals 28d (representing the output value "4") and 28e (representing the output value "8"). Figure 14c shows the rotor 34 rotated to a position to output the value of "7". In this position, the cam followers 62a and 62b on both of the outer contact arms 58a and 58b are operatively engaged by outer camming elements 78, thereby closing the switching terminals 28b and 28c, representing the numerical output values of "1" and "2", respectively. The cam follower 60b on the one of the inner contact arms 56b adjacent the "4" value switching terminal 28d is operatively engaged by one of the inner camming elements 76, thereby closing the switching terminal 28d to yield an output signal value of "4". The algebraic sum of the output signal values of "1", "2", and "4" is "7". The cam follower 60a on the other one 56a of the inner contact arms remains unengaged by any of the inner camming elements 76, thereby leaving open the switching terminal 28e, representing the output signal indicative of the numerical value of "8". Figures 15 and 16 illustrate a rotor 134 configured for use in a ten-position rotary switch. The rotor 134 includes a first plurality of axially-extending inner camming elements 176a, 176b, and a second plurality of axially-extending outer camming elements 178a, 178b. In the illustrated embodiment, there are two substantially conical inner camming elements 176a, and one inner camming element 176b resembling an axially-tapered arcuate ridge. The outer camming elements include three substantially conical elements 178a and two elements 178b having the above-described arcuate ridge configuration. In the ten-position switch, the rotor 134 may be employed with the same spider 42 as is used in the eight-position switch, as described above, but with the inner contact arm 56a associated with the "8" value switching terminal 28e being used, as described below. As in the eight-position switch, the inner camming elements 176a, 176b are spaced from the rotor center by a first radial distance equal to the first radial distance between the center of the spider 42 and the inner cam followers 60a, 60b, and the outer camming elements 178a, 178b are spaced from the center of the rotor by a second radial distance equal to the second radial distance between the spider center and the outer cam followers 62a, 62b. Thus, as the rotor is turned, the inner camming elements 176a, 176b operatively engage the inner cam followers 60a, 60b in a predetermined sequence, while the outer camming elements 178a, 178b do likewise with the outer cam followers 62a, 62b, as shown in Figure 16. The additional camming elements of the ten-position switch, (as compared to the eight-position switch), are needed to provide the two additional output signal values of "8" and "9", both of which require the closure of the switching terminal 28e, corresponding to the output signal value of "8". The closure of the "8" value switching terminal 28e is accomplished by the actuation of the inner contact arm 56a through the operative engagement of the inner camming elements 176a, 176b against that arm's cam follower 60a in the predetermined sequence dictated by the location and configuration of the inner camming elements 176a, 176b. Like the previously-described eight-position switch, the ten-position switch produces output signals indicative of the integral numerical values of "0" to "9" by actuating contact arms to close against their associated switching terminals. This closure is achieved through the engagement of the camming elements 176a, 176b, 178a, 178b with the cam followers 60a, 60b, 62a, 62b in the predetermined sequence dictated by the shape and location of the camming elements with respect to the cam followers. The combinations of switching terminals that, when closed by a contact arm, produce output signals representing each of ten binary-coded numerical values are tabulated in the table of Figure 17 (the format of which is similar to the above-described table of Figure 13). From Figure 17, it can be seen that in the ten-position switch, as in the previously-described eight-position switch, the common terminal is always closed, for all output values, and only the common terminal is closed for the output value of "0". For the values of "1", "2", "4", and "8", only a single switching terminal (in addition to the common terminal), corresponding to the selected one of those values, is closed. For the remaining values of "3", "5", "6", "7", and "9", combinations of two or three terminals (in addition to the common terminal) are simultaneously closed, whereby the algebraic sum of the output signals yields the selected value. From the foregoing description, it will be appreciated that, by using an arrangement of contact arms, camming elements, and switching terminals that allows more than one contact arm to be actuated at a given radial distance from the center of the device (that is, by camming elements sharing a common radius), optimum usage of space is achieved. As a result, higher degrees of miniaturization can be attained than has heretofore been thought practical, without sacrificing durability or reliability. Moreover, the asymmetrical tab and slot arrangement for fixing the spider in the chamber facilitates the assembly of the ultra-miniaturized components constructed in accordance with the present invention, by substantially preventing the inadvertent erroneous orientation of the spider in the chamber. Although rotary switches with eight and ten binary-coded output values have been described herein as exemplary embodiments of the present invention, it will be appreciated by those skilled in the pertinent arts that the principles of the invention can be applied to switches having larger numbers of output values, with relatively minor modifications that will readily suggest themselves to such skilled practitioners.

Claims: A rotary switch, comprising : a housing (22) defining a chamber (26) having an open upper end ; a plurality of switching terminals (28a-e) fixed in the housing (22) so as to be exposed in the chamber (26) ; a substantially planar contact member (42) fixed in the chamber (26) adjacent to the switching terminals (28a-e), the contact member having a plurality of spring contact arms (56a, 56b, 58a, 58b) spaced form each other so as to be individually movable axially out of the plane of the contact member (42) into electrical contact with one of the switching terminals (28b-e) ; a cam follower element (60a, 60b, 62a, 62b) on each of the contact arms, (56a, 56b, 58a, 58b) ; a rotor (34, 134) rotatably mounted in the chamber (26) and having a top surface and a bottom surface, the rotor (34, 134) having an axis of rotation that intersects the contact member (42) at a point defining a center ; and a plurality of camming elements (76, 78, 176a, 176b, 178a, 178b) extending axially from the bottom surface of the rotor so as to be operatively engageable against the cam follower elements (60a, 60b, 62a, 62b) in a predetermined sequence as the rotor is rotated in the chamber ; whereby the operative engagement between a camming element (76, 78, 176a, 176b, 178a, 178b) and a cam follower element (60a, 60b, 62a, 62b) moves the contact arm on which the engaged cam follower element is disposed axially into electrical contact with one of the switching terminals (28b-e) ; characterized in that the contact member has a central common contact finger (50) in electrical contact with one (28a) of the switching terminals, in that at least two of the contact arms have respective cam follower elements that are equidistantly spaced, by a first distance, from the center of the contact member (42), and in that at least one of the camming elements is located a radial distance from the axis of rotation that is equal to the first distance. The rotary switch of claim 1, wherein the equidistant cam follower elements (60a, 60b, 62a, 62b) are symmetrically arranged with respect to the central contact finger (50). The rotary contact switch of claim 1, further characterized by : a plurality of radial detent grooves (74) in the top surface of the rotor (34, 134) ; rotor retention means (80), secured to the housing (22) so as to retain the rotor (34, 134) in the chamber (26), and including a circular aperture (84) through which a substantial portion of the top surface of the rotor (34, 134) is exposed ; and detent means (98, 100), on the rotor retention means (80), for engagement in each of the detent grooves (74) sequentially as the rotor (34, 134) is rotated. The rotary switch of claim 1, wherein each of the contact arms (56a, 56b, 58a, 58b) represents a unique binary bit, and wherein each of the switching terminals (28b, 28c, 28d, 28e) is associated with a unique one of the contact arms (56a, 56b, 58a, 58b), whereby the making of electrical contact between each contact arm and its associated switching terminal can be used to produce an output signal that is indicative of the binary bit represented by that contact arm. The rotary switch of claim 4, wherein the contact member (42) is characterized by : a first pair of contact arms (56a, 56b), each having a cam follower element (60a, 60b) located the first distance from the center of the contact member (42) ; and a second pair of contact arms (58a, 58b), each having a cam follower element (62a, 62b) located a second radial distance from the center of the contact member (42), the second distance being greater than the first distance. The rotary switch of claim 5, wherein the contact member (42) has first and second opposed end portions (44a, 44b), and wherein the first pair of contact arms (56a, 56b) extends from the first end portion (44a) toward the second end portion (44b), and the second pair of contact arms (58a, 58b) extends from the second end portion (44b) toward the first end portion (44a). The rotary switch of claim 5, wherein the plurality of camming elements (76, 78) is a first plurality (76, 176a, 176b) of camming elements that are operatively engageable against the cam follower elements (60a, 60b) on the first pair of contact arms (56a, 56b), and wherein the rotary switch is further characterized by a second plurality (78, 178a, 178b) of camming elements extending axially from the bottom surface of the rotor (34, 134) so as to be operatively engageable against the cam follower elements (62a, 62b) on the second pair of contact arms (58a, 58b). The rotary switch of claim 7, characterized by : a first switching terminal (28e) disposed to be contacted by a first one (56a) of the first pair of contact arms when the cam follower element (60a) on the first one (56a) of the first pair of contact arms is operatively engaged by a camming element (76, 176a, 176b), and that can be used to produce a first output signal value when so contacted ; a second switching terminal (28b) disposed to be contacted by a first one (58a) of the second pair of contact arms when the cam follower element (62a) on the first one (58a) of the second pair of contact arms is operatively engaged by a camming element (78, 178a, 178b), and that can be used to produce a second output signal value when so contacted ; a third switching terminal (28c) disposed to be contacted by a second one (58b) of the second pair of contact arms when the cam follower element (62b) on the second one (58b) of the second pair of contact arms is operatively engaged by a camming element (78, 178a, 178b), and that can be used to produce a third output signal value when so contacted ; and a common switching terminal (28a) disposed to be contacted by the common central contact finger (50). The rotary switch of claim 8, further characterized by : a fourth switching terminal (28d) disposed to be contacted by a second one (56b) of the first pair of contact arms when the cam follower element (60b) on the second one (56b) of the first pair of contact arms is operatively engaged by a camming element (76, 176a, 176b), and that can be used to produce a fourth output signal value when so contacted. The rotary switch of claim 6, wherein the chamber (26) is defined by a substantially annular wall surface, and wherein the switch is further characterized by : contact member retention means (38a, 38b, 46, 48), cooperatively engageable between the contact member (42) and the wall surface, for restraining the contact member form rotation, and for allowing only a single orientation of the contact member (42) in the chamber (26). The rotary switch of claim 10, wherein the contact member retention means (38a, 38b, 46, 48) comprises : a first tab (48) extending form the first end portion (44a) of the contact member (42) ; a pair of asymmetric second tabs (46) extending from the second end portion (44b) of the contact member (42) ; first tab receiving means (38a) in the wall surface for receiving the first tab (48) ; and second tab receiving means (38b) in the wall surface for receiving the second tabs (46).

Inventors: GATZINGER PAUL, NGUYEN THANH, SIMON THOMAS E, GATZINGER, PAUL, NGUYEN, THANH, SIMON, THOMAS E.
Applicants: BOURNS INC, BOURNS, INC.
Application year: 1994
Main classification: H01H19
IPC codes: H01H19